Add FUSE_INIT

This change allows the sentry to send FUSE_INIT request and process
the reply. It adds the corresponding structs, employs the fuse
device to send and read the message, and stores the results of negotiation
in corresponding places (inside connection struct).

It adds a CallAsync() function to the FUSE connection interface:

- like Call(), but it's for requests that do not expect immediate response (init, release, interrupt etc.)
- will block if the connection hasn't initialized, which is the same for Call()

1 files changed, 105 insertions, 0 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index d3ebbccc4..5c6ffe4a3 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -141,3 +141,108 @@ type FUSEWriteIn struct {
 
 	_ uint32
 }
+
+// FUSE_INIT flags, consistent with the ones in include/uapi/linux/fuse.h.
+const (
+	FUSE_ASYNC_READ          = 1 << 0
+	FUSE_POSIX_LOCKS         = 1 << 1
+	FUSE_FILE_OPS            = 1 << 2
+	FUSE_ATOMIC_O_TRUNC      = 1 << 3
+	FUSE_EXPORT_SUPPORT      = 1 << 4
+	FUSE_BIG_WRITES          = 1 << 5
+	FUSE_DONT_MASK           = 1 << 6
+	FUSE_SPLICE_WRITE        = 1 << 7
+	FUSE_SPLICE_MOVE         = 1 << 8
+	FUSE_SPLICE_READ         = 1 << 9
+	FUSE_FLOCK_LOCKS         = 1 << 10
+	FUSE_HAS_IOCTL_DIR       = 1 << 11
+	FUSE_AUTO_INVAL_DATA     = 1 << 12
+	FUSE_DO_READDIRPLUS      = 1 << 13
+	FUSE_READDIRPLUS_AUTO    = 1 << 14
+	FUSE_ASYNC_DIO           = 1 << 15
+	FUSE_WRITEBACK_CACHE     = 1 << 16
+	FUSE_NO_OPEN_SUPPORT     = 1 << 17
+	FUSE_PARALLEL_DIROPS     = 1 << 18
+	FUSE_HANDLE_KILLPRIV     = 1 << 19
+	FUSE_POSIX_ACL           = 1 << 20
+	FUSE_ABORT_ERROR         = 1 << 21
+	FUSE_MAX_PAGES           = 1 << 22
+	FUSE_CACHE_SYMLINKS      = 1 << 23
+	FUSE_NO_OPENDIR_SUPPORT  = 1 << 24
+	FUSE_EXPLICIT_INVAL_DATA = 1 << 25
+	FUSE_MAP_ALIGNMENT       = 1 << 26
+)
+
+// currently supported FUSE protocol version numbers.
+const (
+	FUSE_KERNEL_VERSION       = 7
+	FUSE_KERNEL_MINOR_VERSION = 31
+)
+
+// FUSEInitIn is the request sent by the kernel to the daemon,
+// to negotiate the version and flags.
+//
+// +marshal
+type FUSEInitIn struct {
+	// Major version supported by kernel.
+	Major uint32
+
+	// Minor version supported by the kernel.
+	Minor uint32
+
+	// MaxReadahead is the maximum number of bytes to read-ahead
+	// decided by the kernel.
+	MaxReadahead uint32
+
+	// Flags of this init request.
+	Flags uint32
+}
+
+// FUSEInitOut is the reply sent by the daemon to the kernel
+// for FUSEInitIn.
+//
+// +marshal
+type FUSEInitOut struct {
+	// Major version supported by daemon.
+	Major uint32
+
+	// Minor version supported by daemon.
+	Minor uint32
+
+	// MaxReadahead is the maximum number of bytes to read-ahead.
+	// Decided by the daemon, after receiving the value from kernel.
+	MaxReadahead uint32
+
+	// Flags of this init reply.
+	Flags uint32
+
+	// MaxBackground is the maximum number of pending background requests
+	// that the daemon wants.
+	MaxBackground uint16
+
+	// CongestionThreshold is the daemon-decided threshold for
+	// the number of the pending background requests.
+	CongestionThreshold uint16
+
+	// MaxWrite is the daemon's maximum size of a write buffer.
+	// Kernel adjusts it to the minimum (fuse/init.go:fuseMinMaxWrite).
+	// if the value from daemon is too small.
+	MaxWrite uint32
+
+	// TimeGran is the daemon's time granularity for mtime and ctime metadata.
+	// The unit is nanosecond.
+	// Value should be power of 10.
+	// 1 indicates full nanosecond granularity support.
+	TimeGran uint32
+
+	// MaxPages is the daemon's maximum number of pages for one write operation.
+	// Kernel adjusts it to the maximum (fuse/init.go:FUSE_MAX_MAX_PAGES).
+	// if the value from daemon is too large.
+	MaxPages uint16
+
+	// MapAlignment is an unknown field and not used by this package at this moment.
+	// Use as a placeholder to be consistent with the FUSE protocol.
+	MapAlignment uint16
+
+	_ [8]uint32
+}